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Leaking pipe thread connections

bob young
bob young Member Posts: 2,177
& lampwick on the threads. problem solved


  • Charles_8
    Charles_8 Member Posts: 74

    I'd previously posted about the first gallon or two of hot water being way too hot (from my storage tank heated by the coil). I thought it was thermosiphoning but with more thought, realized that when hot water was drawn, the very hot water in the coil was backing up through the circulator and mixing with the correctly-heated water from the tank. Anyway, this weekend I installed a check valve (swinging-flap) in the line between the circulator and the coil, and now the water temp is constant :)

    However - the only choice at the big-box store was a pipe-threaded check valve. So I got two copper sweat ends, wrapped with Teflon tape and wrench-tight, and screwed them into the valve. Then I soldered the ends to the copper tubing and used a coupling to reconnect to the existing line. Naturally I had a pinhole leak at the coupling, so had to redo that end of the line (and while I had the fitting unscrewed, I used Teflon dope instead of tape). That end doesn't leak...wish I'd done both because:

    There was a very small leak (1/4" deep in a 6" diameter pitcher overnight) from the other threaded end where it screws into the valve! I didn't think the temp of the valve body would get high enough during soldering to melt the Teflon, and the protruding tape isn't discolored or melted.

    So my question is, what's the best way to prevent this?

    1) order a sweat-ends check valve and eliminate the threads entirely (my first choice);

    2) sweat one end, screw the valve onto it, then install the other end (the swinging valve may not end up vertical when the threads are tight?);

    3) sweat the fittings first with tubing stubs, then solder the stubs to couplings (this will still transfer heat to the thread/tape);

    4) a union on each end?

    Any tips appreciated.

  • radioconnection_2
    radioconnection_2 Member Posts: 70

    Unions are the best way. If you solder after doping and tightening the male adapters, they will leak.
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,285
    another fix

    Also available are brass couplings that are male thread on one end and compression (for copper) on the other. I've seen them up to 3/4". Good for wet places ;~)

    Yours, Larry
  • All good advice

    from the pros above . I'll throw another out there - heat up the copper adapters first , and while they're still hot tighten them some more before you solder them . You'll find the adapters somewhat loose after you hit them with heat ( I've found out the hard way too many times ) .
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